Flow through devices are widely used for performing tests of different types. The tests are generally performed on liquid samples which are applied to channels of for example microfluidic size. The liquid sample is subjected to marker and is flowed over an immobilized capture probe capable of capturing marked target components.
Flow through devices are also referred to as lateral flow devices. Lateral flow devices have generally been used as quantitative assay method which can measure one or more analyte species at the same time, with a relative high sensitivity. Generally prior art lateral flow assay has a structure comprising a sample pad, to which a sample is applied, a releasing pad coated with a detector antibody, a developing membrane (typically nitrocellulose) or strip, in which components of the sample move at different rates to be individually separated and to undergo antibody-antigen reaction, and an absorption pad which is provided at the far end of the sample pad to cause the sample to keep moving. The detector antibody is fixed onto, for example, colloidal gold particles to enable the detection. Latex beads or carbon particles may be used instead of gold particles. The diagnostic kit for the lateral flow assay is generally designed to detect an analyte in a sandwich configuration comprising the analyte, the detector antibody, and a capture antibody. Upon applying a liquid sample to the sample pad of the kit, an analyte contained in the sample begins to move from a sample pad. Firstly, the analyte reacts with a detector antibody releasable adhered to a releasing pad to form an antigen-antibody conjugate, which continues to develop in this conjugated form. Then, while moving through the developing membrane, the antigen-antibody conjugate reacts once more with a capture antibody fixed on a developing membrane to form a capture antibody-antigen-detector antibody conjugate in a sandwich form. Since the capture antibody is fixed on the developing membrane, conjugates are accumulated in the area where the capture antibodies are fixed. Proteins are invisible to the naked eye. Therefore, the presence and amount of conjugates are determined by means of an amount of gold particles attached to a certain area of the developing membrane.
The lateral flow assay has been widely and conveniently used in various fields such as pregnancy diagnosis, cancer diagnosis, and microbe detection. However, since quantification cannot be performed with the naked eye and hence an exact amount of an analyte cannot be determined, its application is restricted.
US patent application 2002/0132370 describes a lateral flow quantitative assay method which can measure one or more analyte species at the same time, with high sensitivity. The method comprises the step of binding the target analyte to a capture site and a marker, while simultaneously binding a marked reference compound to a reference site adjacent to the capture site and by use of a laser-induced surface fluorescence detector directed to the capture site quantifying a plurality of analytes.
A method of reading the flow of a liquid in an assay performed using a liquid transport carrier using a photo detector is described in US 2005/0037511.
WO 2004/042403 describes a device and an instrument for the detection of an analyte in a sample, the method for detection of an analyte in a sample comprises the following steps of a) providing at least one particle structure detectable by light scattering and coated with binding entities for said analyte; b) contacting the at least one particle structure with the sample, c) illuminating the at least one particle structure and measuring the scattered light emitted by individual particle structures at least twice and d) determining a change in the spectral signature of the scattered light as a measure of the presence and/or quantity of the analyte in the sample. US 2005/0136500 describes a flow-through assay device capable of detecting the presence or quantity of an analyte of interest. The device contains a substrate printed with a channel to facilitate the flow of a test sample to a detection working electrode. The detection working electrode communicates with affinity reagents, such as redox mediators and capture ligands. For instance, capture ligands that are specific binding members for the analyte of interest are applied to the detection electrode to serve as the primary location for detection of the analyte.
A similar device which comprises an electrochemical biosensor that utilizes detection and calibration working electrodes that communicate with affinity reagents, such as redox mediators and capture ligands is described in US 2004/016190